let arr = [1, 2, 3, 4];
// 1.  for循环 arr2
// let arr2 = arr; // 引用式赋值
// let arr2 = arr.slice(0); // 拷贝
let arr2 = arr.concat();
arr2[1] = 6;
// console.log(arr, arr2);

var arr3 = [{name: "yangmi"}, {"name": "boy"}];
var arr4 = [].concat(arr3);
arr4[1].name = 'list';
console.log(arr3, arr4)